1. Field of the Invention
The present invention relates to a core block used in a number greater than one to configure a single annular magnetic pole core (yoke) through mutual connection of core blocks and to a magnetic pole core for a motor configured through annular integration of the core blocks.
2. Description of the Related Art
In, for example, an inner rotor brushless motor used to drive a motor-driven tool, a sensor for detecting position is attached to a stator and detects a magnetic pole of a magnet provided on a rotor, thereby performing switching control of current to be applied to the stator winding. The stator core of such a brushless motor is configured such that slots between magnetic poles for accommodating windings are opened radially inward. Such a configuration encounters difficulty in winding by use of a winding machine. Specifically, such a winding machine performs winding in such a manner that, while a workpiece is fixed, a winding nozzle is moved along a rectangular or elliptic orbit. Accordingly, the width of a slot between magnetic poles imposes limitation on a usable nozzle diameter or wire diameter. Also, since a space for allowing the passage of the winding nozzle must be provided within a spatial range for winding, difficulty is encountered in increasing the space factor of winding. Inevitably, improvement in motor performance is hindered. Further, the utilization of material for steel laminations used to form a magnetic pole core is lowered.
A known technique for solving such a winding problem is as follows: laminates of core pieces are connected to one another in an articulated structure, which allows bending, and undergo winding in a spread condition; after winding, the laminates are formed into an annular stator core (refer to, for example, Japanese Patent Application Laid-Open (kokai) No. 2000-201458). FIGS. 18A and 18B show the conventional stator core of the articulated structure described in Japanese Patent Application Laid-Open (kokai) No. 2000-201458. FIG. 18A is a plan view showing a step of forming first and second core members by a stamping process. FIG. 18B is a plan view showing a state in which the first and second core members are laminated alternatingly. Each of the first and second core members is composed of a plurality of core pieces connected continuously by connection means (sets each consisting of a convex portion and a concave portion). Opposite ends of each core piece are formed into a convexly arcuate shape or a concavely arcuate shape, respectively. The core pieces of the first core member and the second core member are formed such that one end of each of the core pieces of the first core member is formed into a convexly arcuate shape, and the corresponding end of each of the core pieces of the second core member is formed into a concavely arcuate shape. The thus-formed first and second core members are laminated. The connection means of convex end portions of the core pieces of the first core members and the corresponding connection means of convex end portions of the core pieces of the second core members are engaged with one another, whereby the laminates of the core pieces are connected rotatably. In a state shown in FIG. 18B, winding is performed (not shown) on the arm portions. Subsequently, the laminates of the core pieces are rotated about the engaged connection means so as to form an annular shape. The articulated stator core is thus completed.
Such an articulated stator core has an articulated structure, which allows repeated bending, and enables winding in such a state where the arm portions are caused to project outward one by one. However, in the case of a small-sized motor, forming an articulated structure is difficult or impossible.
Meanwhile, in the case of a split core which does not have connection means employed in the above-mentioned articulated structure, core blocks undergo insulation treatment, followed by winding. Then, the core blocks are assembled together into an annular shape, thereby completing a stator core. In contrast to the above-mentioned winding method in which, while a workpiece is fixed, a winding nozzle is moved along a rectangular or elliptic orbit, the simple split core enables the employment of a winding method in which, while a winding nozzle is fixed, a workpiece is moved. Thus, a thick wire can be readily wound. In this manner, in the case of a simple split core, the core blocks can be handled individually; therefore, winding with high space factor is possible. However, in a process of assembling the core blocks into an annular shape subsequent to a winding process and in a process of inserting the core blocks assembled in an annular shape into a housing, no means is available for maintaining the connected core blocks in an annular shape. Even when jigs are available for such processes, a large number of man-hours are involved. In order to maintain the annular shape without need to use jigs, the core blocks must be fixedly connected by, for example, welding or bonding.
Japanese Patent Application Laid-Open (kokai) No. 2006-304495 discloses a structure which facilitates the connection and fixation of such core blocks. FIG. 19 is a view showing how the core blocks are connected to one another in a fixed condition according to the method disclosed in the publication. The core blocks undergo insulation treatment, followed by intensive winding. The core blocks which have undergone winding are arranged annularly. Then, while adjacent connecting portions are connected, the connected connecting portions are bonded together by use of adhesive. Each of the connecting portions has a shape resembling the letter N, for allowing the adjacent connecting portions to mate with each other.
However, in a state in which such core blocks are assembled without use of, for example, adhesive, the movement of the individual core blocks is restricted, at each connection portion, only in the circumferential direction and unidirectionally with respect to the radial direction. In order to restrict the movement of the individual core blocks bidirectionally with respect to the radial direction and in the axial direction of a motor for retaining the annularly assembled condition, the core blocks must be joined by, for example, bonding or welding. That is, such a split core involves a problem in that the core blocks assembled without use of adhesive or any other joining means are easily separated from one another.
A similar problem is also involved in a stator core of an outer-rotor-type brushless motor (refer to, for example, Japanese Patent No. 3261074 and Japanese Patent Application Laid-Open (kokai) No. H10-210699) and in a stator core of an axial-gap-type brushless motor (refer to, for example, Japanese Patent Application Laid-Open (kokai) No. 2007-028853). Slots between magnetic poles for winding are opened radially outward in the stator core of the outer-rotor-type brushless motor and are opened in the axial direction of a rotational shaft in the stator core of the axial-gap-type brushless motor. Accordingly, as compared with the above-mentioned stator core of an inner rotor brushless motor, not much difficulty is encountered in winding. However, the employment of a split core greatly facilitates winding. Further, the employment of a split core improves the utilization of material in stamping out blanks of a predetermined shape from a steel sheet. As is well known, a magnetic pole core is usually formed by laminating steel sheet blanks of a predetermined shape stamped from a steel sheet. Stamping out an annular piece having the shape of a magnetic pole core leaves a useless central piece having a large area. By contrast, stamping out core pieces of a split core does not involve such useless sheet pieces, thereby improving the utilization of material. From this point of view, even in formation of a magnet rotor core, which does not require winding, stamping out core pieces of a split core improves the utilization of material. However, as mentioned above, core blocks which are merely assembled together are readily separated from one another.